LeetCode-in-All

300. Longest Increasing Subsequence

Medium

Given an integer array nums, return the length of the longest strictly increasing subsequence.

A subsequence is a sequence that can be derived from an array by deleting some or no elements without changing the order of the remaining elements. For example, [3,6,2,7] is a subsequence of the array [0,3,1,6,2,2,7].

Example 1:

Input: nums = [10,9,2,5,3,7,101,18]

Output: 4

Explanation: The longest increasing subsequence is [2,3,7,101], therefore the length is 4.

Example 2:

Input: nums = [0,1,0,3,2,3]

Output: 4

Example 3:

Input: nums = [7,7,7,7,7,7,7]

Output: 1

Constraints:

Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?

Solution

defmodule Solution do
  @spec length_of_lis(nums :: [integer]) :: integer
  def length_of_lis(nums) do
    Enum.reduce(nums, :gb_sets.new(), fn x, gb ->
      :gb_sets.iterator_from(x, gb)
      |> :gb_sets.next()
      |> then(fn
        :none -> :gb_sets.insert(x, gb)
        {^x, _} -> gb
        {y, _} ->
          :gb_sets.delete(y, gb)
          |> then(&:gb_sets.insert(x, &1))
      end)
    end)
    |> :gb_sets.size()
  end
end